An Xbox Live Gold account is required. Choose "Join Game" and leave all the options to "None Specified". Afterward, find a game set to "Pro". If you cannot find one, refresh the list or wait a while before checking again. When you are done, Pro mode should be unlocked for you without having to first completing the game under the Veteran difficulty setting. Note: It is recommended that you first complete the game so you have the "Infinite Ammo" option available. Having the following is recommended: Infinite Ammo Rocket Launcher, Infinite Ammo L. Hawk Magnum, Infinite Ammo Hydra Shotgun, Bulletproof Vest, Melee Vest, and a lot of First Aid Sprays.